Current wireless broadband data communications systems provide high bandwidth necessary for delivering high data rates (and high quality voice, such as VOIP) for both fixed and mobile applications. During a communication session, an access terminal (AT) or station subscriber (either fixed or mobile) may require or desire a connection to a different access network (AN) (sometimes referred to as a resource network (RN) or wireless access point) during a given session. This may occur as a result of the AT moving into a different coverage area or the current session having insufficient bandwidth for the application, or for some other reason. In accordance with some communications protocols, the procedure of terminating and establishing a new connection includes a hard handoff procedure. In a hard handoff, the communication path or session between the AT and the other endpoint is usually terminated or placed in a dormant state before the new path or session is established.
Existing High Rate Packet Data (HRPD) systems function in accordance with interface standards developed by 3GPP2/TIA (3rd Generation Partnership Project 2/Telecommunications Industry Association, namely the HRPD Interoperablility Specification (IOS) (3GPP2 A.S0007-A v.2.0 May 2003), which is incorporated herein by reference. HRPD systems typically employ air interfaces in accordance with TIA-856, while their network architectures are structured according to either the TIA-878 or the TIA-1878 specifications, also incorporated herein by reference. At present, the HRPD and associated specifications do not provide for active packet data session hard handoffs between access networks (AN) in HRPD networks.
Instead, the specifications require the packet data session to be transitioned to the dormant state (basically terminated) before hand off (dormant mode handoff) to a target AN, as described in United States Patent Application Publication No. 2006/0072506 to Sayeedi, et al., which is incorporated herein by reference. The connection between the AT and the source AN is broken resulting in the packet data session becoming dormant. This is done prior to establishing a connection with the target AN. Once a connection is established between the AT and the target AN, the session is re-activated.
The U.S. Patent Application Pub. No. 2006/0072506 states that the approach disclosed therein enables an AT with an active packet data session to perform a hard handoff from a source AN to a target AN without having to force the data session dormant. In an effort to reduce delays in hard handoff, additional A13 messaging (with data session information) between source and target ANs or PCFs is used.
FIG. 1 is a diagram (of representative call or message flows) that depicts an access terminal (AT) with an active packet data session handing off from a source AN to a target AN, in accordance with prior art signaling techniques. Not all flows may be shown. It will be understood that hard handoff procedures within different communications systems or in accordance with similar but different protocols may have different specific call or message flows than that shown. It will also be understood that the occurrence of the source AN/PCF and PDSN A9/A11 messaging flow (for releasing the A10 and/or A8 connections between the source AN/PCF and PDSN), shown in FIG. 1 as occurring after the TrafficChannelAssignment, may occur at other times in the flow, such as described in U.S. Patent Application Pub. No. 2006/0072506.
Referring back to FIG. 1, a blackout period occurs during which data flow between the AT and the source AN is interrupted or terminated. This blackout period is shown in FIG. 1 and generally includes the time period between connection close or termination of the source AN-AT connection and/or source AN/PCF-PDSN connection (which usually occurs around the time of the traffic channel assignment) and establishment of the A10 connection between the target PCF and the PDSN (thereafter establishing an active session between the AT and target AN). As will be appreciated, a hard handoff may occur with or without A13 flows.
During the blackout period, no PCF-to-PDSN connection (RP connection) exists between the PDSN and the target PCF/AN (associated the target AN) and no AT-to-source AN connection exists. Though U.S. Patent Application Pub. No. 2006/0072506 states it is directed to reducing hard handoff delays, it does not appear to address such blackout period.
The blackout period may be on the order of 0.4 to 1 seconds, due to various actions necessary, such as reverse channel acquisition, source/target signaling, traffic channel generation and RP connection establishment. Once the DO or other connection (between the AT and target AN) and the RP connection (between the target PCF/AN and PDSN) are established, the packet data traffic once again flows between the AT and PDSN through the target AN.
During the blackout time period, data packets transmitted from other terminals (directed to the given AT) may still be received at the PDSN. Thus, the blackout period relates to connectivity, not necessarily data flow for the session. Delays in hard handoff and data blackouts may be unacceptable to applications with stringent QoS (quality of service) requirements, such as Voice over Internet Protocol (VoIP), Push to Talk (PTT), Video Telephony (VT) or other delay-sensitive applications. With no RP connection, these data packets are usually dropped. Though resends are possible in some applications, this loss of data is especially troubling in VoIP or other delay-sensitive applications.
Accordingly, there are needed methods and systems that reduce or minimize data loss during a hard handoff in wireless communications systems.